The present invention is directed to a device for damping vibrations, particularly these vibrations associated with structural elements.
Attempts have been made to damp structural vibrations with viscoelastic materials which are known to have a high capacity to dissapate energy, i.e. damp vibrations.
A major drawback to the use of viscoelastic damping materials alone, is their low modulus with respect to structural materials which exhibit quasielastic or quasiresilient behavior.
To overcome this problem, stress supporting or constraining plates have been added to the viscoelastic material on the side opposite the structural element being damped. These plates are usually made of rigid sheet metal, though more recently some thinner, slightly more flexible sheet metals and thermoplastics have been used.
Such a prior art device is described in U.S. Pat. No. 3,399,104 where the daming efficiency of the viscoelastic material is said to be significantly enhanced by the addition of a stiff, rigid constraining plate. The plate may be made of various materials such as aluminum and other sheet metals, wood laminate, metal foils or thermoset plastic sheets.
These devices exhibit several undesirable characteristics, especially when used on a bendable or flexible structural element. Included are the lack of any orthotropic properties in the constraining layer, the unsatisfactory directionality of damping, the unsatisfactory selectivity of damping, the inability to set rigidity and the lack of mechanical linkage between the viscoelastic material and the upper supporting layer. Further, as the supporting layer is made of sheet metal, the prior art devices are heavy. They are also difficult to properly manufacture and are expensive.